3.4 × 10³ N.
Explanation
The perpendicular distance between the 400 N force and the fulcrum is [tex]120 \; \text{mm} = 0.120 \; \text{m}[/tex].
What's the perpendicular distance between the friction of the nail and the fulcrum?
Refer to the diagram attached. The perpendicular distance between the nail and the fulcrum is [tex]0.015 \; \cos{20\textdegree{}} = 0.0141 \; \text{m}[/tex].
What's the size of the friction of the nail?
[tex]F_\text{friction} \cdot l_\text{friction}= F_{\text{400} \; \text{N}} \cdot l_{\text{400} \; \text{N}}[/tex]
[tex]F_\text{friction} = \dfrac{F_{\text{400} \; \text{N}} \cdot l_{\text{400} \; \text{N}}}{ l_\text{friction}}\\\phantom{F_\text{friction}} = \dfrac{400\times 0.120}{0.0141}\\\phantom{F_\text{friction}} = 3.4\times 10^{3} \; \text{N}[/tex].
